C. WHAT CAUSES HIGH NITROUS OXIDE (NOx)?
Nitrous Oxide, also known as NOx, is created when an engine's combustion chamber temperatures reach over 2500F. Vehicle manufacturers have designed several systems, which when working properly, will lower Nitrous Oxide emissions. Below are common high Nitrous Oxides producing failures.
1. Defective EGR System - The Exhaust Gas Recirculation system is designed to reduce NOx. It consists of an EGR valve, vacuum hoses, and one or more vacuum switching valves or solenoids. Later model vehicles may be equipped with electronically controlled EGR valves, which do not require vacuum lines or switching solenoids.
The EGR system's job is to reroute a small amount of exhaust gas back into the intake manifold to help reduce combustion chamber temperatures. NOx is created when combustion chamber temperatures reach above 2500F.
By recirculating exhaust gas back into the intake, a small amount of the air/fuel mixture is replaced with inert gases, reducing combustion temperatures.
2. Faulty Catalytic Converter (CAT) Some vehicle manufactures have designed their cars to operate without EGR valves. Non-EGR equipped vehicles rely heavily on the Catalytic Converter to assist in the reduction of NOx. These vehicles have tendencies to develop CAT problems sooner then those which are equipped. If you own a non-EGR equipped vehicle, and have failed the emissions test for high NOx, pay close attention to the Catalytic Converter.
3. Lean Fuel Mixture - Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers; thus increasing combustion temperatures. This problem can be caused due to vacuum leaks and/or defective fuel control components, such as the MAP, ECT, TPS, and O2 sensors.
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